1. The Field of the Invention
The present invention relates generally earth-boring tools that may be used to drill subterranean formations. More particularly, the present invention relates to shock absorbers for absorbing forces or loads applied to a drill string during a drilling operation.
2. Background and Relevant Art
In various types of earth-boring drilling operations, a drilling machine drives a drill bit or other earth-boring tool, into an earthen formation to penetrate and remove portions of the formation. For example, an earth-boring tool is secured to one end of a drill string, which includes a plurality of tubular members and equipment segments coupled end to end. The opposing end of the drill string is in turn secured to a drilling machine (e.g., drill head, rotary head, double head system) located at the surface. The drill bit is positioned such that the cutting elements located thereon are adjacent the earthen formation to be drilled. The drilling machine may then force the drill bit downward, while also rotating the drill string and the drill bit, in order to penetrate and remove portions of the earthen formation.
Drilling operations may require the use of both longitudinal downward force and rotational force (torque), depending on the type of drilling operation and the material being drilled. Furthermore, during drilling the conditions of the material being penetrated and the bore hole may vary leading to a fluctuation in stresses and forces being transmitted up the drill string to the drilling machine. These fluctuating stresses may include vibration and shock impulses that may present various problems. For example, the shock impulses may cause the drill bit to hop, which in turn may cause the drill bit to cut slowly or unevenly through the formation. Also, the vibration and shock impulses may cause mechanical wear and eventually lead to failure of various part of a drilling system. Each of these problems, and others, can increase the time and cost of the drilling operation.
In order to reduce potential problems due to vibration and shock impulses, shock absorbers can be used to dampen vibrations and absorb shock impulses that are created during drilling operations. A shock absorber, for example, can be a mechanical device designed to smooth out or dampen shock impulses and dissipate kinetic energy. Shock absorbers can include a dampening device that is connected between the drilling machine and the drill string. The dampening device can help reduce the transfer of vibration and shock impulses created during the drilling operation from reaching the drilling head or other parts of the drilling system. Such dampening devices can include some type of resilient material that absorbs the vibration and shock impulses, and dissipates undesired kinetic energy associated with the drilling operation.
One type of conventional shock absorber includes two parallel plates with a rubber disk located therebetween. A driving plate is secured, either directly or indirectly, to the drilling system's rotary drive and a driven plate is secured to the drill string. The plates are typically connected together by a set of fasteners (e.g., screws). As longitudinal shock impulses are transmitted up the drill string, the two horizontal plates are forced together, thereby compressing the rubber disk. The compression of the rubber disk at least partially absorbs the longitudinal shock impulse and dissipates the energy as heat.
While this type of shock absorber may be capable of dampening most longitudinal shock impulses imparted to the drill string, they may not respond to torsional forces and rotational vibrations. In particular, as rotational forces are transferred from the drilling head to the drill string they can be transmitted through the shock absorber. As the rotational forces are exerted on the driving plate, they are can be transferred to the fasteners securing the plates together or even the rubber disks. Thus, a shearing force may be exerted on the fasteners and rubber disks, which can cause damage to the rubber disks. For example, the rubber disks may frequently develop long holes due to friction caused by the screws, which can lead to mechanical failure.
Other conventional shock absorbers can present the same problems or additional ones. For example, pneumatic and hydraulic shock absorbers can be bulky, require additional equipment and systems to properly function, and can be expensive. One will appreciate that the problems associated with conventional shock absorbers discussed above may lead to any number of undesirable consequences. For example, conventional shock absorbers may tend to wear out within a relatively short time, particularly when subjected to large torsional forces. The short working life of conventional shock absorbers may necessitate the need for frequent repair or replacement and thereby may increase drilling costs.
Accordingly, there are a number of disadvantages in conventional shock absorbers that can be addressed.